The art of cast-bonding a cast-in insert formed from an aluminum alloy with an aluminum alloy is known from, for example, Japanese Patent Laid-Open Publication No. HEI-11-107848 entitled “Cylinder Liner Formed from a Powdered Aluminum Alloy”. This cylinder liner formed from a powdered aluminum alloy is intended for enclosing in an aluminum alloy engine block, and the cylinder liner formed from a powdered aluminum alloy and the aluminum alloy engine block are so constructed that the thermal expansibility αC of the cylinder liner and the thermal expansibility αB of the engine block may satisfy 14×10−6/° C.≦αC≦20×10−6/° C. and 1×10−6/° C.≦αB−αC≦8×10−6/° C. Such relationship between the cylinder liner and the engine block in thermal expansibility makes it possible to prevent the detachment of the cylinder liner from the engine block as it does not allow any clearance to be formed between their contact surfaces.
The outer surface of the cylinder liner and the inner surface of the engine block are, however, merely in contact with each other, and do not react or combine with each other.
Moreover, it is likely that when a molten aluminum alloy is poured, its surface may form an oxide film that may be caught and remain between it and the cylinder liner.
Moreover, the engine block increases its inside diameter considerably at a high temperature when the engine is in operation, but the cylinder liner does not increase its outside diameter very much, but becomes loose. For example, the inside diameter Di of the engine block and the outside diameter D of the cylinder liner have a diametrical clearance S of 0.192 mm formed therebetween (S=8×10−6/° C.×300° C.×80=0.192 mm) when their relationship in thermal expansibility is expressed as αB−αC≦8×10−6/° C., when the outside diameter of the cylinder liner and the inside diameter of the engine block are both 80 mm, and when the operating temperature is 300° C. The clearance of 0.192 mm brings about a loose state (JIS B 0401).
According to the related art as described above, therefore, the clearance that is likely to occur between the engine block and the cylinder liner by the oxide film formed therebetween or the temperature of the engine in operation lowers the degree of their intimate contact due to e.g. a decrease in the area of their mutual contact and a reduction in their clamping pressure. As a result, a big difference is likely to occur to the cooling of the cylinder liners. Thus, the related art cannot be said to be perfect.
Therefore, there is a desire for a cast-bonding process that can form an improved bond between a cast-in insert, such as a cylinder liner, and a base material, such as an engine block.